1. Field of the Invention
The present invention relates to a damping force adjusting device for dampers and particularly for hydraulic dampers.
2. Description of the Background Art
Japanese utility Model Registration Application Laid-open No. 3-12034 shows a hydraulic damper for automobile use equipped with a damping force adjusting device. In this device, a coil spring is disposed behind a damping valve mounted on a piston. An operating rod to change the displacement of the coil spring is provided in a piston rod fixed to the piston. Changing the displacement of the coil spring through the operating rod adjusts a biasing force exerted on the rear face of the damping valve by the coil spring, thereby changing the damping force produced by the damping valve.
Another prior art structure has a leaf spring instead of a coil spring and a biasing force exerted on the damping valve by the leaf spring is changed by adjusting the displacement of the leaf spring through the operating rod, thereby adjusting the damping force produced by the damping valve.
In the damping force adjusting device according to the first example of the prior art, the axial length of the coil spring is long, and the axial length of the hydraulic damper also becomes long with a resultant undesirable increase in the size of the hydraulic damper.
In the damping force adjusting device according to the second example of prior art, the load-displacement characteristic of the leaf spring shows a quadratic curve as shown in FIG. 3 hereof, later to be identified. This means that a load changes greatly in response to a small displacement of the leaf spring. As a result, a damping force produced by the damping valve also changes greatly. With this construction, it is difficult to set the damping force to a required value.